Cooking processes utilizing cooking or frying oil at elevated temperatures can result in oxidation, hydrolysis and/or polymerization of the cooking oil. A review of the various deterioration reactions that occur in frying oils was discussed by C. W. Fritsch in World Conference on Soya Processing and Utilization, “Measurements of Frying Fat Deterioration: A Brief Review.” Consequently such oils are susceptible to rapid degradation and the quality, nutritional profile and cooking performance of the oil quickly diminishes. Decomposition or degradation of cooking oil at frying temperatures tends to form free fatty acids and their derivatives, products of the oxidative degradation of fatty acids as well as polymers. The cooking oil also picks up particulates, soluble contaminants such as metal ions and leachates, e.g., food juices, from the food being fried. The presence of such materials in the cooking oil causes undesirable degraded frying properties and also may have a deleterious effect on taste and smell of the food. Specifically, the food fried in such degraded oil may be overcooked with a too dark finish (brown) on the outside before it is properly cooked on the inside. For example, it has been reported in U.S. Pat. No. 4,349,451 that cooking oil with as little as 12 ppm of substances resulting from food juices and/or the interaction of food juices with fatty acids has the undesirable tendency to foam or boil while cooking. In addition, with as little as 6 ppm of such contaminants, the used cooking oil tends to have oleophilic properties with food, thus leaving oily residue on the surface of the fried food product.
Various compositions and methods have been used in the past in order to maintain the quality of the cooking oil or to quickly and economically treat contaminated cooking oil, such as by introducing antioxidants into the contaminated cooking oil. See, e.g., U.S. Pat. Nos. 3,947,602; 4,330,564; 4,349,451; 4,462,915; 5,200,224; and 5,354,570 each incorporated herein to the extent permitted.
It is common in operation of fryers, particularly restaurant fryers, that there is a cycle of oil life from the time a fryer is filled with fresh oil until the oil is discarded as unsuitable for further use. The amounts of antioxidants that are present in the fresh cooking oil are rapidly depleted during heating and cooking at frying temperatures. Oxidation and other degradation reactions, including reactions that degrade the quality of the oil and/or the quality, including taste, smell and appearance, of food cooked in the oil, are amplified at these frequently used elevated frying temperatures. The amount of antioxidants present in fresh cooking oil is limited and inadequate to counteract the rate at which oxidative degradation reactions occur in hot cooking oil. If the amount of antioxidants were greater, the life of the cooking oil would be extended. However, the amount of antioxidants in frying oil is limited because natural oil soluble antioxidants, such as phytosterols, oryzanol, sesamolin, tocopherols and squalene, are generally present in low concentrations. Furthermore, many additive antioxidants potentially suitable for use with food, such as citric acid, ascorbic acid and rosemary extract, have very low solubility or they are insoluble in fresh oil. Therefore the concentration of such stable, nontoxic antioxidants that may be present in fresh oil is limited to low levels. For example, d-alpha tocopherol is added to rapeseed oil at less than 500 ppm and citric acid is used in corn oil and sunflower oil as a process aid at a concentration of 50 mg per kg of oil. Consequently, their presence at low concentrations results in their being quickly consumed when the oil is used at elevated temperatures thereby leaving the oil unprotected. Alternatively, prior methods for introducing such additives included additional components, e.g., mineral particulates, that users may need to filter out of the oil before it is returned to cooking or whose use the food processor may desire to avoid altogether. Other additive antioxidants such as butylated hydroxy anisole (BHA) butylated hydroxy toluene (BHT) and gallates such as propyl gallate, are limited as to the amount that safely can be added to fresh oil because of health concerns. Also, although antioxidant additives such as BHA and BHT are soluble in oil and stable at room temperature, they are unstable and degrade rapidly at cooking temperatures and/or offer minimal antioxidant effect at the elevated temperatures involved in cooking. Consequently, the amounts that may be used typically are limited to low concentrations required for maintaining oxidative stability while the oil is stored prior to use.
The cooking process at elevated temperatures depletes antioxidants in the oil so oxidative degradation progresses quickly. Typically, the addition of fresh cooking oil to used cooking oil introduces into the overall composition only the limited amount of additional antioxidants present in the fresh oil and this is insufficient to provide an acceptable stabilizing effect to the used cooking oil. In circumstances where large volumes of oil are removed from the fryer with the fried food, correspondingly large volumes of fresh oil are required to be added, thereby potentially avoiding excessive degradation of the oil in the fryer. However, other than cooking with essentially fresh oil all of the time, the quality problems described herein typically present problems to the food industry. This circumstance can arise, for example, in some high volume commercial food processor fryers. However, even in these circumstances, the addition of supplementary antioxidant(s) and additive(s) to the oil pursuant to the present disclosure can enhance the antioxidant composition in the oil as well as enhance its cooking performance and the quality of the foods cooked therein. Typically, the quantity of additional fresh oil added to fryers during cooking in restaurants and many retail food production facilities is sufficiently low so that the additional antioxidant from the addition of fresh oil is not sufficient to provide an acceptable stabilizing effect. The result is progressive degradation of the composition of the oil and its cooking performance. Conversely, if the antioxidants depleted by the cooking process can be easily replenished, then the progressive degradation of the oil is greatly inhibited. The resulting benefits can include reduced oil absorption by the cooked food, improved taste and improved shelf life of such food.
Frying studies reported in the literature typically employ test conditions that ignore the influence of food on the frying oil. Some natural constituents or food ingredients have a potential of slowing down the degradation of cooking oil. Water and food acids are common components present in food; in fact, some foods can contain up to 70% water. As reported by C. Gertz et al., studies were performed to simulate and assess the effect of various food components and additives on the stability of frying oils or fats at frying temperatures. In order to simulate the effect of food having been previously cooked in the oil, the presence of water and food acids was represented by the addition of acidic silica gel containing 5% and 10% water. In comparison to the blank (oil heated without food) the formation of deterioration products was reduced in the presence of the acidic silica gel. The polymerization of triglycerides was retarded by acid silica gel in the presence of water. European J. Lipid Sci. Technol. 102 (2000) 543–551, C. Gertz, S. Klostermann, S. P. Kochhar, “Testing and comparing oxidative stability of vegetable oils and fats at frying temperature.”
U.S. Pat. No. 3,947,602 discloses a method for treating cooking oil with a food compatible acid. The method is said to increase the useful lifetime of the cooking oil. However, this method requires heat exchangers to prevent the circulated hot oil from heating the food acid solution to the boiling point. It also requires bulky apparatus and the use of a filter to accomplish the filtering step and thus incurs higher operating cost and capital investment.
U.S. Pat. Nos. 4,349,451 and 4,330,564 disclose a composition comprising water, food compatible acid and porous rhyolite or perlite carrier. This composition can be added directly to used hot cooking oil to remove or neutralize the effect of contaminants, such as soluble food juices and fatty acids in the used cooking oil, to increase its useful lifetime and cooking characteristics. However, it would be desirable to avoid the use of a mineral carrier, as described in these patents as well as in Gertz et al. above, particularly in some European nations where regulations may prohibit the presence of a mineral residue.
Similarly, U.S. Pat. No. 6,210,732B1 claims a cooking oil additive comprising a mixture of citric acid and synthetic amorphous precipitated calcium silicate wherein the mixture is added to heated cooking oil and the oil is subsequently filtered after use of the cooking oil for 6–8 hours. Filtration removes the added calcium silicate as well as food crumbs and other sediment.
U.S. Pat. No. 4,968,518 discloses a process of treating used cooking oil comprising contacting a portion of the used oil with an aqueous solution of a “regeneration agent,” i.e., ethylenediamine tetraacetic acid or n-propyl-3,4,5-trihydrobenzoate, to obtain an oil water mixture and then separating the aqueous components from the oil to obtain a “regenerated” oil that can be returned to service.
A product identified as “Oil Master” was recently introduced to the European market and is said to provide the delivery of aqueous and nonaqueous ingredients by the use of oil as a carrier. It employs an oil soluble emulsifier in order to combine the aqueous ingredient(s) with the oil. The resulting emulsion is added to the used oil. However, this product and its method of delivery uses additional oil as a carrier to introduce the aqueous additive(s). This has the potential of introducing a carrier oil that may differ from oil in the fryer. Furthermore, the carrier oil adds an extra cost for making and distributing the product.
The compositions and methods discussed above as well as others have certain disadvantages. For example, compositions employing activated carbon as an absorbent are hard to filter thoroughly, making it difficult to remove the particles of activated carbon from treated oil with facilities normally available in a restaurant kitchen. Others use filter media and filtration equipment to slow degradation of oil with a filtering step. Others provide for the removal of impurities from the used cooking oil, but do not replenish antioxidants and water in the oil. Still others require long time periods for treatment, which make them economically disadvantageous. Therefore, it would be desirable to provide a composition to overcome these disadvantages by replenishing desirable antioxidant ingredients easily and cost effectively, which composition could be simply added periodically or continuously to hot cooking oil.